Introduction to Physics

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Chapter 1 Introduction to Physics
Image of Sun from STEREO, from NASA.
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1-1 Physics and the Laws of Nature

• Physics the study of the fundamental laws of
  nature
• these laws can be expressed as mathematical
  equations
• much complexity can arise from relatively simple
  laws

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1-2 Units of Length, Mass, and Time
SI units of length (L), mass (M), time
(T) Length the meter (or metre) Was one
ten-millionth of the distance from the North Pole
to the equator Now the distance traveled by
light in a vacuum in 1/299,792,458 of a second
(set by The International System of
Units) http//www.bipm.org/en/si/ Mass the
kilogram One kilogram is the mass of a particular
platinum-iridium cylinder kept at the
International Bureau of Weights and Standards,
Sèvres, France. Time the second One second is
the time for radiation from a cesium-133 atom to
complete 9,192,631,770 oscillation cycles.
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1-2 Units of Length
http//en.wikipedia.org/wiki/Orders_of_magnitude_
28length29
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1-2 Units of Length
There is Plenty of Room at the Bottom Feynmann
http//en.wikipedia.org/wiki/Orders_of_magnitude_
28length29
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1-2 Units of Mass
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1-2 Units of Time
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1-2 Units of Length, Mass, and Time
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1-3 Dimensional Analysis

• Any valid physical formula must be dimensionally
  consistent each side must have the same
  dimensions

From the table Distance velocity
time Velocity acceleration time Energy mass
(velocity)2
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1-4 Significant Figures

• accuracy of measurements is limited
• significant figures the number of digits in a
  quantity that are known with certainty
• number of significant figures after
  multiplication or division is the number of
  significant figures in the least-known quantity

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1-4 Significant Figures

• Scientific Notation
• Leading or trailing zeroes can make it hard to
  determine number of significant figures 2500,
  0.000036
• Each of these has two significant figures
• Scientific notation writes these as a number
  from 1-10 multiplied by a power of 10, making the
  number of significant figures much clearer
• 2500 2.5 103
• If we write 2.50x103, it has three significant
  figures
• 0.000036 3.6 x 10-5

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1-4 Significant Figures
Round-off error The last digit in a calculated
number may change depending on how it is
calculated, due to rounding off of insignificant
digits, might lead to big errors. Example 12.46
6 tax 13.2076, rounds to 13.21 1.76 6
tax 1.8656, rounds to 1.87 Sum 13.21 1.87
15.08 12.46 1.76 14.22 14.22 6 tax
15.07
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1-5 Converting Units
WE WILL NOT DEAL WITH IMPERIAL SYSTEM. YOU DO NOT
NEED TO KNOW CONVERSION FOR THAT.
1 hour 60 minutes 3600 seconds 1 km 1000
m 1 cm 0.01 m 1 mm 0.001 m
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1-6 Order-of-Magnitude Calculations

• Why are estimates useful?
• as a check for a detailed calculation if your
  answer is very different from your estimate,
  youve probably made an error
• to estimate numbers where a precise calculation
  cannot be done

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1-7 Scalars and Vectors
Scalar a numerical value. May be positive or
negative. Examples temperature, speed, height,
your age or weight. Vector a scalar with
direction. Examples displacement (e.g., 10 feet
north), force, magnetic field
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1-8 Problem Solving in Physics

• No recipe or plug-and-chug works all the time,
  but here are some guidelines
• A - Understand The Question
• Read the problem carefully
• Sketch the system
• Visualize the physical process
• Strategize
• B - Solve The Question
• Identify appropriate equations
• Solve the equations
• Check your answer
• Explore limits and special cases

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Bottom Line of Chapter 1

• Physics is based on a small number of laws and
  principles
• Units of length are meters of mass, kilograms
  and of time, seconds in this course.
• Equations must have same dimensions on each
  side.
• The result of a calculation should have only as
  many significant figures as the least accurate
  measurement used in it

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Bottom Line of Chapter 1

• Convert your units to a set of useful ones before
  doing anything else
• Order-of-magnitude calculations are designed to
  be accurate within a power of 10
• Scalars are just numbers vectors are scalars
  with direction.
• Problem solving understanding the problem is
  the main step, read, sketch etc., then see which
  formulas would be useful.